STRUCTURE AND DISTRIBUTION OF DEMERSAL FISH ASSEMBLAGES

STRUCTURE AND DISTRIBUTION OF DEMERSAL FISHASSEMBLAGES ON THENORTHEAST NEWFOUNDLANDAND LABRADOR SHELF

by

oM³GuadalupedelMarVillagarcta

A thesissubmittedtotheSchoolofGraduate Studiesin partialfulfilmentofthe

requirements for thedegreeof Masterof Science

Departmentof Biology MemorialUniversityof Newfoundland

March1995

St.John's Newfoundland

.+.

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Neither the thesisnor substantial extractsfromitmay be printed or otherwise reproduced without his/herpermission.

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a

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ISBN 0-612-13958-1

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TABLE OF CONTENTS

ABSTRACT ••. ACKNOWLEDGEMENTS

LISTOFTABLES ,

LIST OF FIGURES ,.

CHAPTER1.FISHERIESANDFISHASSEMBLAGES CHAPTER2.MULTISPECIESDATAANDMETHODS

2.1GroundfishData ., ..

2.2Methods

iii I, ,j vii 1 6 6 II

CIIAPTER3.CHARACTERISATIONOF THEFrSH ASSEMBLAGES 16

~.1Resultsofthe MultispeciesAnalysis 16

3.1.1 DeepAssemblage 20

3.1.1.1 Description and Environmental conditions20 3.1,1,2Biomass and Species Composition 21

3.1.2 North Assemblage.. . ... 23

3.I.2.t Description andEnvironmental condition s 23 3.1.2.2Biomass and SpeciesComposition 25

3.1.3MainAssemblage 27

3.1.3.1Descriptionand Environmental conditions 27 3.1.3,2Biomassand Species Composition ..,.... 29

3.J.4Coastal Assemblage. . . ... . 32

3.1.4.1 Description andEnvironmentalconditions 32 3.1.4.2 Biomass and SpeciesComposition 33

3.2OceanographyandFishAssemblages ..••.. 35

CHAPTI:R 4.TEMPORAl. CHANGEOF FISIIASSI:M9LAGES 4.1MeanSituation ..,

4.2FirstPeriod :1978·1986 ....

4.3Second Period:1987·1991

38 38 38 44

CHAPTER5.SPATIALCHANGEOFFISHASSEMIlLAGES 5.1 Persistence and Fidelity

5.2 PossibtcCauses .

5.3Final Commentsand FutureWork

BIBLIOGR APHY

49 49 5\

57

59

APPENDIXI.

ApPENDIX 2.

ListoftotalAutumn SpeciesBiomassof each year overthestudy

period 67

Maps showingthedistribution of bottom temperaturesrecorded eachyear intheirgeographicalposition 91

iii

ABSTRACT

Multivariateanalysis of14years of scientificsurvey data has distinguished four groundfish assemblage areas on theNortheast Newfoundland and LabradorShelf.The assemblages werecharacterizedby anhomogeneousfaunal composition,and relative abundance and persistenceevertime.From197810 1986, theirspatial distributionwas maintainedwithincertaingeographicalboundarieswhichfollowed bottomtopographyand exhibitcharacteristicbollomtemperatureranges.Starlingin 1987 and coincident with a declinein thecommercialfisheries,therewas a shiftofthree of the assemblages towards the east. Furtheranalysisrevealedadecreasein biomassin all of the more abundant speciesas wellasin someof theless abundant. Rare species were foundto decrease earlierthandominant ones.perhapsacting asindicators of major changestaking placeacrossthe continentalshelf. Increasing densityof certain species near the shelf/slope break hasproducedgroupingsoffish offshoreofthe main bankswhichhas made themmore vulnerableto the fishery.Possiblecauses forthisbehaviour,e.g.

varyingbottom temperatureandlost of stabilityin themainspecies.areinvestigated.

Intense exploitation ofgroundfi~isthemost likelyexplanationforthedecline of fish biomasson the NortheastNewfoundlandandLabrador Shelf. less abundant species distributionmay alsobeaffectedbydiscardor asby-catchofthecommercialspecies.

Thehomogeneous fishassemblages found couldbeusedas thebasicunitsto managethe shelfin a smallerscalebasisfrom a biologicalperspective and to define highly sensitive areas wherefishlend\0aggregatethat mightneed to be protected.

lv ACKNOWLEDGEMENTS

Iamindebtedineverypieceof my work\0my supervisor,Dr. Richard Haedrich (Department of Biology,Memorial University),for patien-lyguidingme10 builddoubts andthoughtsinto Ihis thesis.Hisperseveranceand optimismhavetold me alessonIwill never forget.

Iamalso very grateful 10Dr.Manuel Gomes(FacultyofSciences, Universityof Lisbon,Portugal) for his guidance inthepreliminarysteps of my researchand his long- distancepresence to answermy numerousquestions.

DavidSchneider(OceanSciencesCentre,MemorialUniversity)was alwaysthere 10spare histimeandmind-inspiringalternativepoints ofview.Thank you!

Iam verythankf ulto JohnHornewho helped my stayin Newfoundland trom the beginningtothe end providingevery information and explanation needed.

Manythan1:s to allthe "4 ClarkPlace"crowd that havehelped mein many differentways. Especialthanksto LynnBusseyandJenniferRobinson for their help withhandlingthemountainsof data.

Thankyou Boyan forsupporting mealongmy work.

Veryspecial thanks 10the staffofthe NorthwestAtlanticFisheriesCentre (Department(IfFisheries&Oceans Canada)whocompiled andmade available the data Ihaveusedin thisthesis.

My workinCanada since 1992hasbeensponsoredby a grant from"La ComunidadCanaria"andfundingfrom theMinisterio deEd ucacion y Ciencia (MEC), Madrid.Spain. Po rtionsofthisworkwereaIM)supported bytheDFO/NSERC Subvention Program,Ottawa, Canada.

Idedicatethisworktomylate brotherGuillermo.

LIST OF TABLES TableI.List of species used intheanalysis.

Table2.Number of yearsthat each species appeared

Table 3.Biomass scale usedin TWINSPAN..

Table4.Numberof stationsby assemblage by year

Table5.Listofspecies thatdefineeachassemblage..

. 10

..14

... •17

.. 18

LISTOF FIGURES Figure2-1.Chart of theNortheast Newfoundland

LabradorShelf...

FigureJ-t.Catch-per-unit effort foreachof the four assemblageareasbyyear Figure3-2.Compositeofallstationsassigned tothe

Deep Assemblage .

Figure3·3.Survey catchratesfor dominant groupsin theDeepAssemblage. , Figure3-4.Survey catchratesforlessabundantgroups

in the DeepAssemblage

Figure3-5. Compositeof all stations assigned\0 the NorthAssemblage.•. Figure3-6. Survey catch ratesfor dominantgroupsin

the North Assemblage Figure3-7. Survey catch ratesfo rless abundantgroups

in the North Assemblage Figure3-8.Compositeof allstationsassignedtothe

Main Assemblage ••• • •• •• • •. ••, •• Figure3-9. Surveycatchrates for dominant groups in

theMainAssemblage...

Figure 3-10.Survey catchratesfor less abundantgroups intheMain Assemblage... Figure3-11.Compositeofall stationsassignedto the

CoastalAssemblage .•. . Figure 3·12. Survey catchratesfordominantgroups in

the Coastal Assemblage .

.. . . . .7

..19

... 20

••• •22

•• 23

... .24

..25

.,••• 27 .28

..•.30

.31

...32

...34

vii Figure 3-13.Survey eaten rates(orlessabundant groups

in the CoastalAssemblage... ...•.. , Figure 3-14.The Labrador Current systemand its

relation tothe Newfoundland area...,

.. . ..35

.... ..36 Figure 4·1.Approximateareasoccupied bythefour

fish faunalassemblages 39

Figure5·1.Mean bottomtemperatures recorded at survey

stationsin each assemblagearea by year .54

CHAPTERi, FiSHERIES AND FiSHASSEMBLAGES

Depletion (Hilbornand Walters, 1992) anddeclineoffishstocks around the world (Messieh,1989;Frechet,1991; Ludwig etet.,1993) inthelast twenty yearshave pointedoul the need toknow the distributionof fish atdiversescalesof study (Dalley andAnderson,1993).Without such information,itwill beimpossible to achieveabetter knowledgeof theocean'scontinental shelves whoseecosystemsprovide us with mostof the world' s fishresources.

Thecontinentalshelves inthe Northwestern AtlanticOceanare among the most extensiveandproductive areasinthe world forcommercia l fisheri es. Historically , marine fish populationshave beenconsideredtoovast10 bedepletedbyharvesting (Rosenbergetal.,1993) ,and this wasessentially sofortheNewfoundl andfisheries . Theresult isthatnationaland internationalfleetshaveexerted a very strongfishing effort on the stocks there foralmost five centuries.

In1977,withthe extension of Canadianjurisdictionalwaters10 twohundred miles,Canadianfisheriesbiologi stswerefacedwith the verydifficult task of applying stockassessmentproceduresacrossthe continentalshelves. Theyhadto managethe fishing groundswithouthav ing much scientificinformationonthefish population dynamicsovera veryextensive area. The size andscale oftheshelf was itself a problem. TheNAFQdivisions2 and 3themselvesextend over 350,000square kilometers(Murphyand Bishop,1993) and haveavery abrupt topographyand complex physicaloceanography. Surveyand commercialdata were takeninto accountto seta totalallowablecatch (TAC)eachyearin orderto maintainthestocks;studieswere

carried out onaspeciesby speciesbasis. Thetechniquesused werebasedon the estimationofmeans oftotal abundance and associatedvariances (Smith,1990)using the standardformulae forstratifiedrandom design ste.g. Cochran,1977). Overtheyears, furtherimprovement of theparametersused inthe models produced better estimations (CochranandEllner,1992).

To achieveabasicknowledge ofthe spatial and temporaldistributionof the speciesseemed tobethe firstapproach required to improve the existingmodelin order totake furthermanagementdecisions(Dickieetal.,1987). Suchan approachwouldbe possible on the continentalshelvesof thePaci fic coastof the UnitedStates and Canada wherestudies from a groundfish assemblage perspective have beencarriedout(Gabriel and Tyler,1980),andsimilarstudiesareunderway in the Norwegia nDeep[Bergstad, 1990) and ontheGrand Banksof Newfound land(Gomes, 1993). ButtheNo rtheast Newfoundlandandlabradorshelf,the areaofthe northern cod stock, has neverbeen studiedfromthisparticular pointof view and scale.

Inthelate 80'sand beginningof the 90'sa progressive declinein theabundance of thefish stocks throughdivisions 2Jand 3K onthe Newfoundlandshelf suggestedthat groundfishspecies distributionalchangesmightbeat work;variouspossibilities such as overfishingor migration couldaccountforthe changes,but a spatialapproach was necessarytocharacterize thedistributio n patterns and their dynamics. Thefishing grou ndsoffNortheastNewfoundland andLabrador coast arehome to a number of kinds offish,and groundfishare themaintargetof thefisher ies. The lack of selectivity of some of thefishing gear usedproduces very diversetows (i.e. containing a good mixture of species)so it seemed reasonabletoapproach the fisheriesona multispccies level;

obviously,knowledgeof eachspecies'ecologyisnecessary 100,butthe two different approaches(individualand multispecies) may complementeach other (Pielou, 1974) and together helptobetterunderstandthefisheries ecosystem.

Groundfishcommunitieshave beenshowntobequitestable andexhibit distinctive assemblages that are generallyaligned withthebottomtopography.Rogers and Pikitch

(1992) detected six major groundfishassemblagesoffthe coastsof Oregon and Washingtonbased on consistencies inthree types of analysis of the speciesweights;

Colvoco ressesand Musick(1984) foundconsistentlyfive groundfishspeciesassociations onthe MiddleAtlantic Bightcontinentalshelf over ac-yearperiod;Mahon and Smith (1989) describedthedistributionof the ScotianShelfand Bay of Fundy demersalfish assemblagesandfound them tobe stableandpersistentthrougheighteensurveys (twelve in summerandthreeeach in spring and fall)but havingdifferentoutcomesat different clusterscales;O..erholtzand Tyler(1985) found thatthe spatialintegrityof each assemblage onGeorges Bank was preservedover timein spiteof changes in species richnessandrelative abundance; Gomes (1993)studied sixteenyears of Spring surveys ontheGrand Banks of Newfoundlandand found groundfishassemblageswhich were pcrsistantandhomogeneous. TheNortheastNewfoundlandshelf hasnever been investigatedin such a holisticmanner (Atkinson.1993) and to do so is one motivebehind this thesis.

A fisheriesbiogeography ofthe shelfshouldprovidea spatialdescriptionof groundfish distribution and discloseareaswith homogeneous species composition and biomass that,if persistentoverthe years.have the potentialto become the basic managementzonesthat are of a size that is comfortable to monitorandregulate;changes in these areas oughtto be detectableearlier than at thelarger scale ofthe whole continentalshelfscale. Such areaswould be based on a multispcciessamplingand analysis.and therefore would consider species biomassinformation importantregardless of whether the species were commerciallyfishedor not. Several environ mental variables.suchasbottom topography,depth.sedimenttype,latitude andbottom temperature. have beenreported to be related10 species area boundaries(Colvocoresses andMusick, 1984; Mahon and Smith,1989; Gomes etal..199 2);therefore. such investigationsmay also disclosepossiblerelations betweenthe distributionpatternsof assemblagesandenvironmentalgradients or variability.

Forthis study.theDepart ment of Fisheries and Oceans (DFO) made available

fourteenyea rs of Autumngroundf ish sampling data, a numberthatencompasses the generation time ofsome of themost importantgroundfishontheshelf;itseems therefore plausiblethatspecies areas,iffoundover tha! durationof timeon anannual basis,can be assumedto be quite stable.NumerousauthorsfecI that the turnover time mustbethe minimum valueofyearssampledinorder0 obtain acceptablevalues; moststudiesthat display stab ilityinthefishassemblages haveonlybeenstudiedfor2 to4years without allowing natural variability10appear(Rogers and Pikitch,1992).Ihave adoptedthe generation timeas a good indicator based on Gomes'study(1993) done onthe.nearby Grand Banksarea which is inhabitedbyquite similarspecies.Nevertheless,theresults obtainedfromtheanalysescan onlybe indicative of the groundfishdistribution relative to the catchinggearused (demersaltrawl)andthe seasonof the year whenthesurvey was done (Autumn)(Doubleday andRivard, 1981;Pitt etal.,1981).This implies some biassince thetiming ofthe surveycruisesvariedslightly from year10yearandthe environmental conditionsin theareamayhave somewhatalteredthe generaltrends that fish followin theAutumn whenthemain commercialspecies,mostlyAtlantic cod, migrate offshore.

I have namedthe areas whichIidentify"fish assemblages",ater m definedby Tyleretel.(1982) based solely on geographicdistributionand by Underwood(1986)as ahaphazard groupof populations of various speciesthathappen to be togetherat any placeand time withouttakinginto account trophicrelationships.Among the species of an assemblagethere may be,of course,importantand complexinteractionsthatare worthwhilestudying. Therefore,the next appropriatestep would beto try tofind possiblerelationshipsamongth~componentsoftheassemblage (Underwood.19 86)to see iftheyrepresent a true biologicalcommunity.Atfirst I hadhopedtobeable to address this matter butseveralcircumstanceskept me from achievingthiscomplextask:

firstly,the lack oftime to finishitwithin~itelimitsof aMaster's thesis;secondly,the results obtainedby Gomes etal, (1992) which showeda high degree ofuncertaint y in the r-ttcomesoftrophicinteractions,and, finally thefinding that the shelfecosystemis

extremely complex inthis area and that thereareinsufficientdata tocome to anyfully conclusiveresults(Shelton etal.1993.1993).

Inspite oftheabove hindrances,I havebeenableto address mostof my original hypothesesusinga multispeciesapproach. I have found thatthere are fourgroundfish assemblageswhose speciescompositionand abundanceremain fairlyconstant. These havebeen described.They are presentpersistently over thefourteenyears of study and theyseem to be well-aligned to thebottomtopography. During the first 9years ofthe dataset ,the grc undfishassemblagesdescribed keptwithinfairly narrowgeographical boundaries,but thcyseem to haveunder gonemajor changes duringthelast five years.

Thisperiod,ofcourse.was the one during which thefisherybasedontheNorthe rn cod collapsed. Thusthestudy affordedan oppon unity not only 10 describeandcharacterise the fish assemblages of averylargeandimportantregionofCanada's Atlantic continentalshe lf,butalsotoinvestigatethe spatialandtemporal dynamicsoffish assemblagesduring the periodof amajorfishery collapse.

CHAPTER 2. MULTISPECIESDATA AND METIJODS

2.1 GreundrishData

TheCanadianFederal Departmentof Fisheriesand Oceanshas beenconducting Autumn groundfishsurveysoff Newfoundland and Labrador since1977. The zone coveredcorrespondsto sub-areas2 and3 of the Northwest AtlanticFisheries Organization(NAFO)andspecifically 10divisions 2J and3K(since1978) and 3L (since 1981).Thedataused in this study were collectedfrom 1978to 1991duringthe Autumn, mainlylate Octobe rto earlyDecember. inthe 2 divisions (2J3K)that correspondtothe areasknown as theNortheast Newfoundlandand Labradorshelf(Fig.I).

The researchvesselR.V.GADUSAn.6,NTICAconductedthesurveys during the entire14years;a stratifiedrandom method wasused ongroundfishsamplingsurveys withstratificationbylatitude,longitude and depthin therangefrom100to1,000metr es.

Samplingstationswere allocatedto strata accordingto area withall strata containingat least 2 stations.Towswereusually of 30 minutesdurationat 2.5 knots witha 29-mm mesh linerused in the codend ofthetrawl (Atkinson,1993). Surface temperature, bottom temperat ureat the endof thetow anddepth ofthe tow (mean and maximum) were alsorecorded.

For eachyear,a two-waydatamatrix was constructedconsistingof anentryOJ) that represents the catch inweight ofspeciesjat stationi. Species wereincluded initiallyintheanalysisonlyiftheirbiomass comprisedatleast 0.05 %ofthetotal catch in thatyear'sAutumnsurvey.

Screening of the completespecies list was necessaryforseveralreasons. Some

Figure 2·1 , Chartof the NortheastNewfoundlandand Labrador Shelf. with place names usedin the textindicated ,NotealsoNAFO Divisions2J,3K and3L.

identifications were incomplete.beingonlydone to familyor genus level. Also,a numberofspeciestaken inadvertentlyinthe demersa ltrawlswere pelagic,Therefore, some otherrulesforinclusion were alsoestablished,Specieswere excludedif:

I) thedata onlyincluded identificationtofamily andwith insufficientbasis forspeciesidentification.

2) they were pelagicspecies,except for capelin(MallofUs villosus)and Arctic cod(Boreogadus saida)whichpla y an importantroleindemersal food webs.

3) they were very largespecies suchas Greenlandshark(Somniosus microcephalus)or Baskingshark(Cetorhinusmaxi/lllls) whichappeared very rarely in trawls but couldgreatly biasthe analysis because oftheir immenseweight.

4) their totalbiomassanQabundancewere tess than0.05% of thetotalfish caug htinthatassemblage.

5) they were absentmore than 5 yeal'S out of the14 sampled,except for specieswhoseabundancew:bio mass was lessthan 0.05%, in whichcase the species shouldappearin more than2 contiguous years.

After applyingthe aboverules ,a totalof 35 species(Table1)remained tobe used in thefinalanalyses;the numberof speciesrangedbetween 28 and 35 per survey,with 29 ofthem (Table2) almostalways present.

Following identificationof the assemblages,afun her revisionwas done by assemblage and year10trytoidentify whichspecies were mostrepresentativeofthe catch in each assemblage. Summaries ofthe basic species data finallyused- by species, year,and assemblage- arefoundinAppendixI.

TABLE 1:Listofspecies used in theanalysis of groundfishsurveys.

Commonname Alligatorfish, Northern Capelin Cod,Arctic Cod, Atlantic Cod,Greenland Dogfish,Black Eel, Longnose Eclpout,Arctic Belpou.,Esmarck's Eelpout, Vahl's Grenadier,Roughhead Grenadier,Roughnose Grenadier,Roundnose Flo under,Witch Hake,Blue Halibut,Atlantic Halibut,Greenland Lumpfish,Common Lumpfish,Spiny Marlin Spike ,Common Plaice,American Redfish, DeepWater Redfish,Golden Sea Raven Sculpin, ArcticDeepsea Sculpin, ArcticHookear Sculpin,Moustache Sculpin,Shorthorn Skate, Smooth Skate,Spinytail Skate, Thorny Tapirflsh,LargeScale Wolflish,Broadhead wotfflsh, Spotted Wolffish,Striped

Scjentlncname Agonusdecagonus Mallofll5 vitlmus Boreogadus saida Gadus morhua

Gaaus

Myoxou phalllJscorpius Raja setua Rajaspmicauaa Rajaradiata Notacanmuschemnitzil Anarhicnas denticulotus Anarhkhasminor Anarntcnaslupus

10

TABLE2:Species listedinTableI,withthenumberof timesthat thespecies appeared duringthe yearsund er study andthe yearswhenthespecies was absentindicated.

Not presentin Number

or

Scientificna me --'-_ _ -'- "'- _

Agonusdecagonus Anarhlchas denticulatus Anarhichas minor Anarhlchaslupus AntimorarOSfrafa Artedieitusuncinatus Boreegadussoldo CentroscylliumjabriclJ Coryphaenoidesrupestrts Cottunculusmicrops Cycfoprerus lumpus Sumicrotremusspinosus Gadusmornua Gad us ague GIYPlocephaluscmogtossvs Hemtmpterus amencanus Hippog/o.uoit/esplatessatdes Hippog/ossus hippoglossl/s t-ycoaesesmarki Lycodesreticuloms Lycodesvahttt wocrounuberg/ax MallOlllsvi/foslIs Myoxocfp"alu.~scarptus Nezumia baird!

No/aeal/thuscllellln/tzii Rajaradtata Rajasenta Raj a spinicQuda Reinhardriuship[Joglossoides sebastesmarinas Sebastesmen/ella Synapllobranchllskaupi Trachyrllynchusmurrayi Trfglopsmurrayf

14 14 14 14 13 11 14 13 13 12 14 14 14 10 14 6 14 13 10 14 14 14 13 10 14 12 14 14 14 14 14 14 12 6 13

7'

7 '

7B 81.'3

86,88,90,91 78-81,'3-85,90

9D 82,83,85,86

78 80.B1 ,85,87

78,81

78,81 78·82 ,84,85 ,89

86

II 1.2Methods

Forevery Autumnsurv eytherewasa log-transformation of literawcatchdata ofspeciesjatstation ; to avoidhaving themost abunda ntspeciesdominatetheres ults of themultiv ariateanalysis. Previousexperienc e wi1h groundfishdata (Gauch.1982;

Gomes,1987)indicated that thelogarithmictransformatio n In(1+x) did not change the outcomesign i fican tlyas compared10 the rawdataanalysis.

Ordinat ion wa susedtorepre sent catchandspeciesrelationshipsin alow- dime nsionalspace(Gauc h andwhittaker.1981)andhiera rchical classificationwasused toplace catchesintogroups (Piclou, 1984). There are2types ofhierarch ical classification:Agg/flmt' rtl lil'(,classificationbegins withindividualhaulsand progressively combinesthem,andDi v;.!il'!'classification begins withallthehau ls and progressively divides them. Ecologistshavedefendedthepracticaland theoretica l advantagesofusing polytheticdivislve methodsasopposedtoagglom erativeones(Boesch, 1977 ; Gauchand Whittaker,1981;Gauch,(982) . Thelaterhave theoreticaladvantagesin that all the availableinformation isused tomake thecriticaltopmos tdivis ions,re sultingina classification thai isles s sensitivetoinfluencebythe rand om"noise" commonlyfound inecological samples(Lambert et al.,1973citedin Gomes , 1993 ) .

Hillera1.(1975)propo sedapolythetlcdivisivemethodbased on anordinat ion techniqueunde r thenam e of"indicatorspeciesanalysts". Thismethodhasbeenrefi ned and computeri zed byHill(1979 )asTWINSPAN;thesoftwareisdesignedtoconstruct two-wayorde redtablesandthemethodofdoing soisbyidentifica tionof differen tial species. Adifferentialspeciesis defined asonewithclear ecological prefere nces,so that itspre senceca n beusedto identifyparticularenv ironmentalconditions.

The aim orTW INSPAN analysis is10thro w thesalientfeatu resof the data into sharprelief,bygroopinglikespecies withlike,andlikesampleswith like.Stations are classified first andthespecies areclassified secondacco rding totheir ecological preferences,using theclassifica tion of the statio nsasa basis. The basicsteps ofa TIVINSPAN analysisare:

12

1.-Classifythe stationsinadivisi vehierarchy,dividingthemfirst into2 subsets,then 4,8,16,etc.

2.-Convertthe stationclassificationinto an orderingora rank.

3,-Using the groupsof stationsas abas is,construct attributesforthe species, i.e."

preferential 10the right side of themajordivision"."prefere ntialtheleft side of the seco nd division",etc..

4.-Classifythe speciesinthe samewayas thestations, but with thediffer encethat whereasthespec ies weretreated asattribu tesofthestatio n s, tilespe cies have attributesof the kind indica tedabo veinstep3.

5.- Co nvertthe speciesclassificatio n into an orderingor a rank.

6.-Print out theresulting ordered two-way table,withstationsas columnsandspecies asrows.

Thebasic activityofTWINSPANis to makea dicho to my. Theprogra mdivides upthestations into gro upsbyre peated dichotomization,anddoesthe samefor the species. TWINSPANmakesitsdichotomiesinamannerbroadlysimila rto that describedbyMueller-Dcm boisand Ellenberg(1974).They recommendeddividingthe speciesinto threecatego ries, preferentialtothele ft,preferential to therightand those that are indifferent. Mainlybecause it canbearguedthatdichoto mies donot arise naturally,these categories arenearlyas arbitrar y asdividingthespeciesin two (preferential to theleft and to therightasin TWINSPAN) ,sinceindiffe rence and preferemiatityare amatterof degree. The stagesof creatinga dichot omyin TWINSPANare asfollow s:

1.-Identify adirection of variation inthe databyordinatin g the samples. Thisis referredtoas'pri mary"ordination andis madebythemethod of reciprocal averaging(Hill,1973).

2.-Divide theordinationat itsmiddle to geta crudedichoto myof thesample s.

13

3.- Ide ntify differential speciesthat are preferenrialtoone sideorthe otherof thecrude

<lichotomy.

4.-Construct animprovedordination,referred to as a "refined"ordination,usingIhe differentia!species as abasis.

S.- Dividethere linedord inationatanappropriate point to derivethedesired dichotomy.

6.-Construct a simplifiedordination, the"indica tor"ordination,based ona few of the mosthi ghlypreferentialspecies, and see whether the dichotomy suggestedbythe refined ordinationcanbereproduced byadivisionof the indicatorordination.

Withthe exceptionof borderlinecases,the refinedordination is used to determine the dichotomy. TWINSPAN introduce s also the term "pseudospectes"in orderto accountfor different"le ve ls"of abundanceor biomass inthe samples.

Theidea of the di fferentia lspecies mentionedin stagc 3 is essentiallyqualitative, but tobeeffecti ve with quantitativedataitmustbereplaced by a quantitativeequivalent.

This equivalentiscalleda"pseud ospecies" (Hillet al., 1975; Hill,1977),The essential idea is that much of the quantitat ive informationcan be retained by expressingit on a relativel y crude scale suc hastheBtaun- Blanquet scale of cover-abundance(Mueller- Dombots andEllenberg,1974;WesthoffandMaarel.1973).The levels of abundance usedin TWINSP AN to defineIhe crude scale arehere termed"pseuoospeclescutlevels".

Inthis study I examined fish catches and thereforea biomass scale was construc ted.In order to introducethe valuesinto TWINSPAN ,six pseudospeciescut levels wereusedbased ona biomass scalecoveringthe availabledata (Table3), The valuesof thecut levels(0,5 , 5, 25, 125,625 and 12(0 ) wereconvertedinto logarithms (by10(1 +x» tobe comparablewiththe contentsof the data in theinput matrix.

The num be rof pseudospeciescutlevels shouldrepresenta compromisebetween thea prioriobtai nableinformationfrom the dataand the availabilityof computer space and timesinceeach pseudospecles is stored separatelyin thecompute r.Themethodof pseacospe cles allowsqua ntitativevaluesto be used as diffe rential"species' and as

14

indicators. Thus, wewillnot have Atlantic Cod(Gadus morhua)as a differential species, having instead Cool if the biomassishigher than0.5 kg), COO2 ifit is greater than5 too, Cod3 ifis greaterthan25 and soon as differential species.

Table 3: Biomassscale withcut levelsused in TWINSPANin this study.

BIOMASS RANGE (KG) CUT LEVEL

0.5 ·5.0 0.40

5.0 -25.0 1.79

25.0·125.0 3.26

125.0·625.0 4.84

625.0 -1200.0 6.44

>1200.0 7.09

As anexample.followingthescale shownin Table3. imaginethatstation 1 has a catchof SOO kg of cod(Gadusnmrhuo)whereasinstation2 only100kg ofcodwere taken.These valuesdifferbya factor of 5 but with an applicationof the cutlevelsused in this analysis.the followingpseudospecieswillbepresentin the stations:

STATlONI(500 kg): Codt(0.40),COO2(1.79), Cod3(3.26) and Cod4 (4.84) showing therefore4 pseudospecieswithinthesinglespecies cod,

STATION 2 (100 kg):Cool (0,40), Cod2 (1.19)and Cod3 (3.26) having3 pseudospecteswhich in fact are in commonwith the 3prese nt in station I,

Inspiteofthe difference in weight (5 toI),thestationsare registeredbyTWINSPAN ashavingmorein common(hanthey doby way of difference,

is

Thefinalresults ofTWINSPAN aredisplayedinatwo-waytablethatfulfils requirementsof non-exc lusivity. An ubiq uitousspecies canthereforebe associated with more than one groupingof stationsby simplevisualinspection. Clusteranalysis (CLU STAN: Bray-Curtisindex , Group Averagemethod)wasalsousedfortileyears 1978, 1979and 1980;examinationoftheTWINSPANtwo-wa y tables allowedthe recogn itionof biological featuresof eachof the main station gro upsfirstid entifiedby thiscluster ana lysis.Such featuresincludednot on lythediffe rentialspecies(t.e.species havingclear preference fora given cluster)but alsothepresence orabsenceof a very widesp readspecies in acluste r, or ano maliesindusterrichness (numbe rofspecies presen t).These charac teristicsareusedto classifystationslaid offthe mainclustersor 10rati fyIheclassification ofthose ambiguous sta tions usuallylocated on geo graphical bounda ries oftheareasoccupie d bythe mainstationgroups.Theusc ofTWINSPAN allowedthe de rivation ofmoreinformati o nfromthe data than did the clusteranalys is, andfor datafrom19 81onwards TWIN S PANwasusedtoalloc ate stat io ns tofish assemblages.

Once the two-w a y(ableproducedbyTWINSP ANfo r eachyearwas analyzedin detail,stations were assigned to theas semblage s of speciessho wnbythe results. Geograp hicalcon tinuitywasche cked and the data we re mappedusingSIGMA PLOT and SPANS (GIS).

16

CHAPfER3.CHARACTERISATIONOF FISHASSEMBLAGES

3.1 Rl'Su\lsoftheMnllb pecies Analyses

The TWINSPAN analysisof the fa-yea rserie s of biomass surveydata, comp risinginall3,520trawlstations, identified4differentassemb lages(Deep,North, Main and Coastal)that appeared10 recurregularly inthe area (Table4). Each assemblagewas characterizedby its ownspecies compositionand abundances;

nonetheless,a numberof ubiquilousspecies appeared in severalof the assemblage descri p lions [fable5).

Itwasnecessaryto distin g uish two different periods overthetimecourse ofthe investigation. Duringthe first9years (from 197 8to19 86),the assemblagesend10 occupythesamegeograp hicareawithslig htdirrerencesamongthe yearsso (hal lmean situationcouldbeidentifi ed(seeFig. 4-1).Startin gin 1987 andcontinuinguntilthelast yearinthedataseries (1991),the geog raphicposiricn oftheassemblages changed drastically and itwasnotpossible to describeanymeanspatialdistrib utionforlhemany more.Theareasoccupiedbyoneassemblagehad been "invaded"byanotherassemblage whichhad extendedbeyonditsmean distributionasfoondinthefirstperiod(1978-86);

otherassemblageshad"shrunk"in respectto thespatialareatheyoccupy,and, in particularzones,certainassemblagesha devenlost someofthei rmaincomponent species.

With respecttothecatchper uniteffort(CPUE),the mostproductiveassemblage wastheDeeponewithameanCPUE forallthespeciesof 330kg/tow(s.e.45) showing its maximumin1981wit h67Bkg/towand minimum in 1989with115kg/to w;theleast

17

productive wasthe Coastalonewit ha meanof96kg/low(s .e. 15)exhibiting219 kg/tow in1978and4 kg/lowin 1991asitshighe st andlo westvalues. TheMain and North Assemb lageshad intermediateCPUEs of 281 kg/tow(5.c.26)and265 kg/towts.e.34) withmou ima of 5 71 kg/towin 1983 and439kg/tow in 1986 and minimaof 180 kg/tow and 19 kg/tow,respectively(Fig. 3·1).

TABLE 4: Numberofsta tionsbyassemblageand year forthe periodof stud y,1978- 199 1; inbracketspercentageof stationsassignedto each assemblagewithin each year.

LastTOWshowsthetotalnumber of stationsbyassemblage fOTtheentir e 14 years.

ASSEMBLAGE."EAR DEEP NORTH MAIN CO A STAL

1978 7(5 . 6 ) 42(33.6) 67(53.6) 9(7.2)

1979 34(16.1) 54(25.6) 119 (56.4) 4(l,9)

1980 42(17.6) 66(21.6) 111(46.4) 20(8.4)

1981 42(18.8) 65(29.0) 95(42.4) 22(9.8)

1982 55(18.2) 74(24.4) 134(44.2) 40(13.2)

1983 30(11. 7 ) 84(32.8) 117(45.7) 25(9.8) 1984 36(13 . 7 ) 41(15.6) 134(51.! ) 51(19.5)

1985 50(15.3) 79(24.2) 131(40.2) 66(20.3)

1986 21(9.8) 55(25.6) 95(44.2) 44(20.4)

1987 26(9. 0 ) 72(25.0) 115 (39.9) 75(26.1)

1988 21 (8.8) 73(30.6) 83(34.7) 62(25.9)

1989 14 (5.1) 61(22.1) 118(42.7) 83(30.1)

1990 20(8 .2) 33([3.6) 84(34.6) 106 (4 3.6)

1991 24(7 . 7) 50(16.0) 108(34.5) 13 1( 4 1.8)

TOTAL # 422 849 1,511 738

18

TABLE5:List ofspeciesthatdefineeach assemblage according to presence and catch per uniteffort.

ASSEMBLAGE DEEP NORTH MAIN COASTAL

CPUE(kgltow)

DeepWlllu Alll\ntic Cod Alll1nl i~Cod

Redfish

>100 DeepwaterRcd fi ~h

--

Greenland AmericanP lllice GreenlandHali hu! Ath'nlicCod Hlllih ul

Brcm1head G",en hllld

Round"'>$<! Wnlffi~~ Ha lihul 10 - 100 Grena dier

Or""nl11llll Ame,; c.."

BlOlIdh".d H..lillu! Plaic"

Wol ffi~h

Roullhhelld Spotted Goldenaedfi.1t ThornySbte . Gr" n" di"r Wnl m ~h

AmericllnPl llice Black DogfiAA SlripcdWol ftio<h

Wi:chFloonder

1·10 ThnTn)'Skll1e

Br""dhclld

RC>Uj:hhelld WoW;.h

Grelladi"r

BlueHak" Wilc h F loundcr Slrip"dWolffi.h ArclicCod.

A!'elicCod Arclic Eelpullt Witch

Marlin Spike ^{Flou nder}

Sl"'ue dWolffh h

<1 Arctie Eelrnll!

ArclicCod

Thereseemed 10 be agoodcorrespondence between the distributionofthe assemblagesand thebottomtopography of thearea. The NENewfoundlandand Labrador shelves(NAFOntvistons2Jand3K) arevery profuse in banks(Harrison,

19

800~---~

79 80 8182 83 84 85 86 87 88 89 90 91

YEAR

1 -

-+-

I

Figure 3·1.Catch-per-uniteffort (kg/tow,allspecies)for eachof the four assemblage areasbyyear.

Hamilton,BelleIsle, FunkIsland), saddles (Cartwr ight, Hawke),basins (e.g. 51.

Anthony)anddeep s(e.gFunkIsland).This co rrespondenceagreeswith theliterature on fish assemblages mentionedin Chapter1.and see mstohea commonfindinginall studiesdone on the mailer.

20 3.1.1 DEE P ASSEMB LAGE

3.1.1.1Descr jpttonand Emoironrnenta lconditions

As thenameindicates,stationsthat belonged to this assemblage were situatedin the deeperareas of the Northeast Newfoundla ndand Labrador shelves(Fig,3-2).The assemblage occupiedanelo ngated area in

bothNAFO Divisions2Jand3Kloca ted ..

= ,---

along theshelf-slopebreak at latit udes ranging from 55°30'Nto 49°30'Nand longitudes from 55°30 'Wto 50oW.The ~ Deep Assemblage was the only one that maintained its spatial distributionduring the entire 14years ofstud y, and also showed certain stability and little variation 51 in the environmentalvariablesstudied.

Thenumbe r ofstatio ns assignedto

theDeepAssemblageranged from7in q .I-::=~2:;l2;:::;:::;::~:0::::1

1978 to 55in 1982witha mean of 30

Figure3-2, Compositeof allstations (SO=13) stations peryear. From 1978 assigned to the Deep Assemblage, 1978.

unti11982 there was an increasi ngnumber 1991 of stations surveyed that showed

characteristicsof theDeep Assemblage,but from 1982 to1989 the number decreased dramaticallyonly increasingslightlyto 24 stations in the assemblage in 1991. The mean depth fluctuated between 688±39 metres(SE) in 1991 and 349±17m in 1978;i334 min 1979 was the deepest station surveyed during the 14 years and 231 min.tC}g2 was theshallowest. The greatestrange in anyone year was in 1979 with stations at depths between1334and 233 rn.

The mean bouorn temperatures werethe warmest values of allthe assemblages withtemperature means from 4.18± O.29°C(SO) in1983 10 2.66±1.21 °Cin 1979,

2\

reflecting the quilt: stablebottom temperature in this area. The wannest individual station was foundin 1991(S.J0qandthe colder ones showed a temperatureof O·Cin differentyears.In 1983.1988and 1989the mean bottom temperaturewaswarmer than average,and1980and 1984 were colderyears.

Mean surfacetemperaturein the area of theDeepAne mblagewascalculated even thoughitprobablyshouldnotbeconsideredvcry irnponant as regardsgroundfish analysis.Valuesranged from 2.97±1.24°C(SO)in 198010O·C(50=0) in 1991 with the warmestindividual stationsurveyedin1979a.o°C)andthe coldestin19 84 (.1.2°C). Theyears1978, 1984 and 1989 exhibitedcooler than average temperature s whereas1979.1980and 1988werewarmer.

3.1.1.2 Biomassand SpeciesComposition

The catchperuniteffort ofthis assemblageexhibitedadecreasing (rend from 1978to1991. Incertainyears, theCPUEappeared 10increase but thiswas dueto seoastesspecies (mainlySt'bostt'smt'n1~lIa)whichwere occasionallytaken in enormous quantities(orderof 11 IOns) insome towses~iallyin 1983,1986 and1988.

Excludingthese unusualredfishlows.CPUEin theDeepAssemblagehad a declineof 500 kg/tow inJ4 years varyingbetween610 kg/tow in 1978 and110 kg/tow in 1991 with a meanof 3?oO±46 kg/tow(SE).This assemblageexhibiteda biggerdecrease than the others.butthis couldbedue 10the highnaturalvariationin the catchabilitythat characterisedthedeepwaterredflsh(S~b(IJr~s1Ilt'n1t'lIa),a dominantspecies.The mean CPUEof the wholeassemblage showedno significantdifferenceamong years,with the exception of thestrongredfish year1981;when the unusual tows ofredfish were removed, any differencedisappeared.

Deepwaterredflsh(St'hasfesmemetknwasthemostabundantspecies withCPUE valuesgreaterthan 100kg per tow.Greenlandhalibut(Reinhardfillshippoglossoid~s) was thenextmost abundantspecieswith CPUEsthatwere between20 kgpertow in 1989 and100kg pertow in1986.when itcomprised25% ofthe total catchinthe

22

Dominant species- Deep Assemblage 4OOr-- - - - - - - - - - - - --,

1

0100

°

• DEEPWATERREDFISH !IilGREENLANDHAUBUT

• BROADHEADWOLFFISH mJROUNDNOSE GRENADIER

Figure3-3. Survey catch ratesfOTdominant (andcommercial)groupsin theDeep Assemblage.

assemblage(Fig .J.3).

Broadhead wolflish(AnarhichQJdrnricu!oftlJ)wasaveryimportantspeciesinthe DeepAssemblage100,showing aCPUEbetween10 and40kgpertow;itwasmo st abundantin191 8 and 1980.AIaboutthe same levelof abundanceandcharacteristicof this assemblage inconsiderableamounts wastheroundnosegrenadier(Coryphaenoides rupesrris),with CPUEranging (rom20to70 kgperlOW (Fig.3·3).

Roughheadgrenadier(Macrourusberg/ax)andblack dogfish(Cemroscyllium labricll)werean orderofmagnitudeless abundant in theDeep Assemblage with CPUEs rangingfrom4 1015kgpertow (Fig,3-4)Bluehake(Amimorarosrom;and marlin spike(Nezumiabairdill were always presentinthisassemblage butinvery small

23

Less abundant speciea- Deep Assemblage

12~---, 10

.g

'"

'" 6 ui

~

U

79 80 81 82 83 84 85 86 87 88 89 90 91 YEAR

• BLACKDOGFISHffijBLUEHAKEIIIMARLIN SPIKE Figure3·4.Surveycatch ratesfor less abundant(andnon-commerctaljgroups in the Deep Assemblage.

quantities, i.e.lessthanIkg pertow duringall [4 years.

3. 1.2 NORlll ASSE MBLAGE

3.1.2.1Descr iptionandEnvironmentalcondillons

The NorthAssemblageoccupiesmainlyNAFO Division2Jbutin someyears extends southwardinto3K(Fig.3-5). Itcomprisesanarrow area north of theMain Assemblage andlatheeast of the Coastal Assemblage.From1978101987itlies within thelatitudes from 50⁰45'N 10 55"30'Nand longitudes between57°30'W1053oW;after 1987. theassemblage shifted slightlytowardsthe north and east tolatitudes between 51"IO'Nand55"30'Nin1987,1988 and 1989 but between53°15' N and55°30'Nin

24 1mand 1991andlongitudes between S6°12'WandSr2$'w inallthese five years.

Ameanof60 (50= IS)stations 501

per yearwerefound 10 fall within this assemblage. The lowest numberof stationsinanyone yearwas 33(in1990) iii

and thehigheslwas 84 (in1983). In general, the NorthAssemblageincludes anincreasingnumber ofstations from

,

..

Dominant speclea- North Assemblage

500~---~

;t400~.... ... ... ... .• ..• : .. ... . .. .. ..

I

~300

82 83 84 8586 87 88 89 90 91

YEAR

.WOLFFISH

IIAMERICAN PLAICE

I!!JATLANTIC COO

~GREENLAND HAUBUT figure3·6. Survey catchratesfordominant (andcommercial) groupsinthe North Assemblage.

the surface temperature,Thewarmestyearswere1979,1980,1982and 1985 whereas the coolest were1978.1984 and1991.

3.1.2.2BiomassandSpecies eompcsltlon

The CPUE in the North Assemblageranged from438.6kgrtow in 1986to18.58 kgflowin1991. A massivedecline was detectedin1990 and199 1 when less than 50 kg/towwere takenas compared with themean overallof265±34 kg/tow(SE). The catch was 400kg/lOW in 1978, decreasedto250 kg/towin1981,andthenincreased progressivelyuntil 1986where 438.6 kg/towweretaken.From1986 onwards,thecatch per unit effortdecreasedsharplyshowinga CPUE of only 18.58 kg/tow in 1991.

26

Atlanticcod(Gadusmorhuo)is oneofthe principalspecieswithinthisassemblage until1989 (a mean of about150kg/low).From 1989 the CPUE for this speciesshows adeclining trendto arrive atnearly0kgrtow in1990and1991 (Fig.3~6).Itcomprises a high percentage of thetotalin the catches for the NorthAssemblage(around50%

before1989 and30%thereafter).

Greenlandhalibut (Rtlnhardtiushippoglossoides)showeda CPUEof about40 kg/tow until 1988, withthe exceptionof 1984 when amea n of110 kg/tow wastaken.

From 1988 onwards a sharpdecreasewasfoundwithvalues of lessthan 10 kg/towin 1990 and 1991. Neverthelessthepercentagein eachyear' scatch ofGreenlandhalibut withinthe Nonh Assemblage remained mostly around20%. Americanplaice (HippogfossoiJtsplatessoldes)wasanotheroftheimportant speciesinthis assemblage.

Itshowedvaluesof CPUE around 60 kg/towuntil 19:i4 butthese decreasedto 2 kg/tow in 1991. However,aswiththe Greenland halibut,thepercentagecomprisedbyplaice overthe years remainedvery stablearound15%.

Deepwaterredfish(S('ho.lfe.~memello)was anotherNorthAssemblagespecies thatshoweda decreasingtrend inthe catch,especiallyfrom1988onwards.But.aswas mentioned above. redtishappearedvery erraticallyand.though60 kg/lOWwerecaught in 1978, the general trend showeda mean of 10 kg/towuntil1987 andredfish were nearlycompletelyabsentfrom \988until1991. Broadheadwolffish(Anorhichas denriculatus) showedthe sameas theotherspeciesthatpredominated inthis assemblage

• a decliningtrend from 1984onwards(Fig. 3·7) but again withthe percentagewithin the totalcatchevery year quite constantaroundabout8%. CPUE forthis large wolffish species was around25 kg/towuntil1984 and about8 kg/towfrom 1985fromthen on until the last year of the studywhenonly 2 kg/towwerecaught.

Spottedwolffish(Anorhicho.rminor)andstripedwolflish(Anorhichoslupus)were speciesthat appear inthe Nonh Assemblagebut inlower percentages,about 3% ofthe totalcatchforthe year;in1991.a slight increasewas noticeableinboth species, amounting10 5% and10%respectivelyof the totalbiomass caught.ThornyskatetRoia

27

Less abundant species - North Assemblage

1 4,--- - - - -- - - - --,

'2~·· · ·····=;· ·· · ····· ····· ······ ···· I

~

F e

w

::l

!3

°78 79 808182 8384 85 868788 89 90 91 YEAR

. THORNY SKATE IJIGRENADIER

fIDWlTCHFLOUNDER fiillARCTIC COD

Figure3-7 . Survey catch ra tes (or less abundant(and non-co mmercia l)groups in the NorthAssemblage.

radiara)androughheadgrenadier(Macm /lmsberg/ax)areNorthAssemblagespecies withaCPUEofabout3 kg/low. Arctic eefpout(Lycooesreticukuusi,witc hflounder (Glyp'ocephoJu.~cynoRlo.u/l.f)andArcticcod(BnreogaJussaidu)represented onlyaround Ikg/lOWofthetotalcatchof the assemblage each year.

3.1 .3MAINASSEMBLAGE

3.1.3.1DescriptionandEnvironmental conditions

TheMain Assemblagewastheprincipal assemblageinrespect to the extentof area occupiedandthenumber of stations sampledeach year(Fig.3-8). From1978 to 1986,the assemblagewas locatedatlatitudesbetween 53°30' Nand49°30'Nand

28 longitudesfrom 54

ow

Beginning in 1987 end continuing thereafter its extent shrank to occupy 55 longitudes onlybetween 53°24'W and SooW.At the same lime.there beganto appear areas within this assemblagethat 53

had characteristics of the Coastal Assemblage(see below). These"holes"

werelocalized atlongitudes from 51"to 53"W andlatitudes between 52" and so 52°30' N,50°30'and 51⁰³⁰'N and 49"30'and SooN. The resultwas that theMain Assemblage came to cover a

smallerarea,

:~~~:e1-~~ theC:~S~S:~b~~C,S~~~~~

There was a mean of t08 1991.

(50=20)stations peryearwithin the

Main Assemblage,with theminimum of 67 stationsoccurring in1978 and a maximum of134 in both1982 and1984. Theshallowestmean depthofthe stationsthatbelong 10 the MainAssemblagewas 287 min1978 and thedeepestwas 382metres in1990 For individualstations, the shallowestwasin 1978 (191 m) and the deepestsampled was 863 min 1990. The greatestdepthrange was in 1990(222-863m.84 stations) and the least was found in 1978 (202-400m,67 stations).

The mean bottomtemperature ranged from 1.75°Cin1985to 3.11 °C in1980 , with the greatest scope in 1983 (0.9-5.8°C).Therewas a generaldecreaseinmean bottom temperaturefrom1978 to 1985 from 3.1°Cto 1.75°Cand then a gradual increase103.09"Cin1991. Mean surface temperatureranged from O°Cin199110 3.11"Cin1980 , with a slightly increasing trend from 1978 (2. 19°C)to 1980 (3.11°C) . From 1980 onthere was a generaldecrease with some ups anddowns to endup at O°C

29

in1991due tothe freezingconditions.Thehighest surfacetemperatureranges were foundin 1979.1980and 19S2withranges of 7.4,7.0and 6.0·Crespectively;for individualstation s.7.rc(980)wasthe wannest encounteredin this area inallyean while·l.O·C was the coldest and recordedin1979.

3.1.3.1Biomass andSpedesCom position

The Main Assemblage.byits characteristic speciescomposition as well35byits meandepth ofthestations.resembledverymuchtheNES Deep Assemblagedescribed by Gomes (1993)for theGrandBanksofNewfoundland.This appreciationwasobvious because the MainAssemblagecould bedescribed asa prolongation to the north of Gomes'assemblage(fishdo notknow aboutthe NAFOareas!)withslightdifferences in the relativeabundanceof certain species.The MainAssemblagewaslimited to the east bythe Deep Assemblage whose border seemed to marktheapproximate limitsof distribution ofAtlanticcod,AmericanplaiceandwitchRounder. Deepwater redfish increased in relativeimportancewhenmovingfromtheMain to theDeepAssemblage to theeast.TheMain Assemblagewaslimitedby theNorthAssemblageto thenorth and nonhwestandby the CoastalAssemblageto the west.

Atlantic cod wasthemost abundant speciesintheMainAssemblage (Fig.3-9) with a meanCPUEof140kg/towoverallyears. There seemed tobeageneral decreasingtrendfrom 1978(100kg/tow) to 1988 (50kg/tow)butin1986there is some recovery (l70 kg/towlthatcontinues in 1989.1990 and1991060kg/tow). AIthe beginningofthestudyseries. this speciesrepresented about35%in weightofthe total catchbutby the last yearsithadbecome mostof the catch(78% in1991).Thisfact probablyresultedfrom the disappearanceofmanylessabundant species,especiallyfrom certainareas as wasmentioned earlier(sec.3.1).

Deepwater redfishin theMainAssemblageexhibitedavery highCPUEbetween 1978and 1981witha mean ofabout 425kg/tow.The value dropped to 125kg/tow between1982and 1988andended up at only10kg/tow from 1989 to1991.Deepwater

30

Dominant spsclea - Main Assemblage

500~---~

400

-a,300 ~

.x

gI200

a.

o

100

o

YEAR

_ATLANTIC CODOOlOEEPWATER REDFISH1I0 REENLAND HALIBUT Figure3-9. Survey catch rates for dominant (and commercial)species in the Main Assemblage.

redfish represented on averageabout 30%in weightofthe totalcatchoverallyears,with exceptions in1983 (60%) and1988 (45%)whichwereinkeepingwith theinterannual variabilitycharacteristicofthisspecies. GreenlandhalibutCPUE showed an increasing trendfrom1978 when 20kg/tow weretaken to1986 with 75 kg/tow. From1987, however,the speciesstarted to declineinabundancetoreach an average of15kg/tow during the rest of theperiod of study. Greenland halibut representedabout15%in weightof thetotalcatchover the years. Goldenrcdfish exhibited an abundance of 50 kg/tow in 1980 and30 kg/tow in1983, butfrom1984 on declined sharplyto 5kg/tow (it should be emphasizedthat theidentification of thisspeciesmay not be very satisfactory due to its similaritywith the Deepwaterrcdfish;in some casesthisdifficulty

3'

resultsinbothspecies being classifiedunderthe generic -Redfish spp.-).

Americanplaice and witchflounderwerespeciesthaidisplayeda verysimilar behaviourthroughout allyearsinthisassemblage(Fig.3-10).Bolhspecieswere present in the sampleswithaCPUE around 20kg/towin1918(21 and 17kg/tow respectively), bothmoweda decliningtrenduntil 1991wherethey only were caughtin values of5and 2kg/to w,andbothrepresented amean of7" inweightofthetotalcatchbyyear.

Broadhead wolffishshows thesame declineasthese Iwospecies;ithad a CPUEof 14 kg/lOWin1978while in1991itspresence was barely 2kg/tow.Thisspecies comprised 5%ofthe totalweight in theMainAssemblage overthe yearsofstudy.

Less abundant species - Main Assemblage

80 ,---- - - - - - - - - - - - - - ,

0

1

78 79 80 818283 84 85 8681 88 89 90 91

YEAR

• WOLFFISHES !!!JEELPOUTS IIIAMERICANPLAICE§lWITCH FLOUNDER

Figure3-10.Survey catchratesforlessabundant(usuallynon-comrnerctal) speciesin theMainAssemblage.

Figure J·11. Compositeofallstations assign edto theCoastalAssemblage,197 8- 1991.

32

Thorny skateand rougbbeadgrenadierwerepresentatalower order of magnitude (Fig.3-10),representingonly around5 kg/lOWin 1978 anddecreasing to 2kg/tow in the formerand 10 Ikg/tow in thelatter.These speciescomprisedonly2%ofthe weightof the total catch overthe years.Other speciesthat appearedinverylow abundance were striped wolffish,Arctic eelpout,spotted wolffish and Arctic cod in descendingorde rof abundance.

3.1.4COASTAL ASSEMBLAGE 3.1.4.1Descr-lptien andEnvironmenla lcond itions

The CoastalAssemblagehaditseasternborder withtheNorth Assemblageinthe northandthe Main Assemblageillthesouth (Fig. 3-11). It had thelowest species diversity of anyassemblage. andseemed

tobe associa tedwiththeinshore colde r branch ofthe Labrador current. The Coastal Assemblage did not appear conspicuouslyevery year,for exampleas in1979,but inotheryearsit occupiesan area even large rthan that ofthe Main Assemb lage itself, for exampleas in 1984. Theprimary differencebetween this assemb lage and the Main Assemblage, apart from Ihe low abundanceanddiversity,was the absence of all the wolffishes (Broadhead, spotted and striped). The Coastal Assemblage coveredan elon gate area alongthecoast inNAFODivisions21and 3Kbetween

latitudes49°30 'N1055°30' N duringall 14years of the study; from1978 to1986 it fell

33

011avengebetWttfllongiludes53"3Q'Wto 57"3Q' W,but from 1987 101991itextended itsstationstothe east10longitudesrangingfromS2"30'W1057"30'W and occupying thr"holes" leftbythe shrinking oftheMain Assemblage;in1991there were even some CoastalAssemblagestationsatSI"W.

Thenumberof stationsintheCoastal Assemblagewastenerallylowerthan averageuntil1984 bUIfrom 1985thenumberincreasesrapidly;therewereonly four stationsin1978but therewere 133in 1991,witha mean of 53 (50 =36)stationsper lear.This wastheshallowestassemblagewith meanyearly dePthsbetween 178 m and 274m;for anindividual station theshallowestvaluewas in 1989 at103mand the deepestwas in1991at 494 m.The greatestdepthrangewasin1990(116-485m)and the leastin1979(148·240m).

Themeanbottom temperaturefortheCoastal Assemblagerangedfrom -O.85"C in1984 to 1.3°Cin1991with individual stationextremesof -1.9°C in 1984 and 4.1°C in1991. Thislast yearalsohad the greatestrange ofindividualbottomtemperatures wilhvaluesbetween..0.7and4.1°C.Themeansurfacetemperaturerangedfrom O°C in 1978.1984 and 1991to1.4°Cin 1981. Thewarmest temperature recordedwas 3.9·Cin 1989andthe coolestwas_1.2°C measuredin1984;thegreatestrangewas found in 1989withsurfacetemperaturesbetween-0.4 and 3.9· C.

3.1.4.2BiomassandSpectes Composilion

Greenland halibut.Atlantic cod andAmericanplaice wert the main components oftheCoastalAssemblage (Fig.3·12).Thefirst speciesshowed a mean CPUEof50 kgltowexcept in1978 whena CPUEof 125kgltowwas recorded. TheGreenland halibut CPUEdeclined1010kg/lOWin1984 and increasedslightlyfrom1985until1991 wherea mean of15kg/ tow occurred; itspercentageby weightstayed mostlyaround 20% withseveralyears of highercatchin 1978(57%),1980 (45%)and1990(65%).

Atlanticcod was anotherimportantspecies inthisassemblage. Ithadan increasing trend incatch rate from40 kg/tow takenin 197810about 95 kg/towin 1985

34

Dominant spec ies - CoastalAssemblage

200

1

~¹⁰⁰

o .0

°78 79 8081828384 85868768 89 90 91 YEAR

_ATLANTICCODII!lAMERICAN PLAICEIIIGREENLANDHALIBUT Figure 3-12.Survey catchrates for dominant(and commercial) species in the Coastal Assemblage.

and1986. Thereafteritdecreasedto only 5 kg/tow in1990 andrecovered slightly in 1991to25kg/ to w; in spiteof thesechanges,cod consistentlyrepresentedaround the 50%inweightofthespecies thatmakeupthe CoastalAssemblage.Americanplaicehad aCPUBaverageof40kg/tow until 1985. but in1986 this value was reduced significantlyto 10 kg/towand after1987 only 4kg/lOWwere takenas a mean peryear.

Plaicere presented around 20% in weight until 198 6, and from thai yearonwa rdonly 10%ofthe totalcatch per yearwas comprisedbythis species.

Tho rny skate,Arcticeelpout, witch flounder andArcticcod were mino rspecies always presentinthe CoastalAssemblage butin very low abundance(Fig. 3-13). They allshowedvaluesof CP UE lessthan 3kg/ towand repres ented nomo re thanI%in

35

Less abundant speclea - Coastal Assemblage

79 80 81 8283 84 8:588 87 88 89 90 91

YEAR

.THORNY SKATE I!J!jARCTIC COO IlIIWITCH FLOUNDERIiIDARCTIC EELPOUT

Figure 3·13.Surveycatch ratesforless abundant (andnon-commercial)species inthe Coastal Assemblage.

weightof the totalspeciescatch in anyyear.

3.2Oceanogra phyandAssem blages

The Northeast Newfoundland Shelf isoneof the threemajorpartsof Newfoundland' scontinentalshelf, and is the widestcontinentalshelf outsideof the Arctic. Itis about300 km wide and1500 kmlong, withan averagedepth of about 200m. Manyof its numerousinshore embaymentsare deeper than200m. Theoffshore partof the shelfpresents several banksofabout 300m withthebasinsreaching 500m in some areas (Helbigetal..1992).The shelf is widerandshallowertotheSouth where itformsthe GrandBanksofNewfoundland andis narrowerandmore complextowards

36 theNorth whereitconstitutes the labradorShelf.

The LabradorCurrent(Fig.3·] 4) dominatesthe NortheastNewfoundland and LabradorShelf;itis the presence of this maier currentthat gives the shelfits polarcharacteristics,with temperatures

belowzero and salinitiesaround 34·35 ...·~~ril----T~::;:!:o---j ppt. Itis composed ofthree.different

water types that meet near the northern lipofLabrador,i.e. Arctic waterthat comes throug htheHudson Strait, Arctic water from BaffinBay and a fractionof waterfrom theWest GreenlandCurrent, Two distinctbranchesofthe Labrador currentarefound onthe LabradorShel f:

the offshorebranchflows parallelto a polarfront that extendsalongthelength

of the shelf and is trapped on the

~:ui~ :;I~~~nTt~et~b~~;:o;~~~~~=:;:~

continentalslopeand gelling stronger

overthe 6OOm-800misobaihs (speedof 80 cm/s)and theinshore branchwhich is weaker (e.g. surfacespeedofIOcm/s) and itis evidentin the upwardslopingisohalinesoverthe shelf Il.azler,1982;Helbig etal., 1992).

Whenthe LabradorCurrenlreaches the Northeast Newfoundlandshelf,mostof the offshorebranch remainsbathymetricallytrapped overthe continentalslope flowing on tothe southaround the GrandBanks to tum west to the northofthe GulfStream system;the other branch remainsinshore,partof it goingthrough theStrait of Belle Isle (Petrieand Anderson, 1983) and intensifiesuntil reaching theAvalon Channeland finally roundingthe southerncoastof Newfoundland(Helbiget al.,1992).

37

The main offsho re branchofthe LabradorCurrentcarriesthe greatestvolume of water.ltls re lativelywarmandsaline(temperature of 3to4"Candsalinityaround 34.9 ppt). Itseemsto beassociatedwith theDeepAssemblage andcontributestothequite stablebottom temperature s observedthere.

TheMain Assemblagealsoseems10be associatedwith the LabradorCurrent main branch. Bottomtemperatures of this assemblageareabovezerothough lowerthan foundintheDeepAssemblage,probablydue tothe presenceof the polar front.

Theinshore coldandfresherbranchof the Labrado rCurrent(temperatures of _I0

to2"e andsalinityor 32.Sto 33.5 ppt)can be re latedtothe Coasta lAssemblagewhich shows a lowdiversity ofspecies:the possiblechangesin the extension of the inner branchduring thecoldyearsof theSO's may accountforthe expans ionto the eastofthe CoastalAssemblage. Theincreasing presenceofspeciesquitetolera nt tolo w tempe ratures,suchas Arcticcod(Lillyetat., 1994)or Arcticeelpout(Fig.3~13).in this assemblage may reflect this expansion.

TheNor th Assemblageexhibitsa mixof waters withcharacteristicsofbo th branches of theLabradorCurrent.Thisis probablythecase because itoccupiesthe area ofthe DeepAssemblage tothe northandcertainareasinshoreto thesouthwhichrun parallel tothe inner branch ofthe Labrador Current; nevert heless, the bottom temperatureassociatedwith thisassemblagewasmainlypositiveindicatinga greater affinityto the offshorebranch.TheNorthAssemb lage did not extendsouthwardsinthe lastyearsof study,asituationwhichmay alsobe due 10the insho rebranc hexpansion across the shelf.

CHAYfER4.TEMPORAL CHANGE OF FISIIASSEMBLAGES

4.1MeanSlt uallon

Duringthetirst 9years ofstudy,the fo urassemblageswe refound inrecurr ent areaswith slightdifferenc esfromyeartoyearpres umablydue tothe inherentvariability or theecosyste m;nererore. ageneralsituationcanbepresentedwhereinthegeojlraphic positionofthe groupsof statio nsthatrepresent each ofthefishassemb lages of the NewfoundlandandLabradorshel fisplottedusingthedatafromtho seyears(1978-1986) asrepresentativeofthemosttyp icalsituation(Fig.4·1). Persistence over timeofthis sorthasbeenfoundbystudes offishassemblagesindifferenloceans (Colvocoressesand Musick.19&4; Tyler et al.,1982;OserholuandTyler.19 85;Maho nandSmith,198 9 ; RogenandPikitcb,1992).

Slarting in1987.however.amean pictu recanno longerbede scribedfor Newfoundlandand Labrador.asinaronwhichcould becaused.probably.bya lossof global stabilityinthesystem;inthesela st five yearsthesystem seems to bechanging towardsadiffe rent alternativestability (WaltenandHolling.1990).Sincetheslability ofacommunity dependsontheenvironment in whichitextss aswellasonindivid ual densitiesandspeciescomposition,the spatialvaria tioninthefishassemblage areas could berelated10 physicalaswe llaspopulation parameters that mayhavechanged significanl1yinthe periodbeginningin1987.

4.2first Period: 1978·1 986

Despite thefactthaiameansituationhasbeendescribed.anomalie sappear in

39

56

55

54

53

52

51

50

49

2J

3K

58 56 54 52 50 48

Figure4-1. Approximateareasoccupied by thefour fishfaunal assemblages on the Newfound land-LabradorShe lf:Coastal,Nort h,Mai n. andDeep.

thespatia ldistributionas well as thedepth andtempera ture ran ges foreach assemblage ona year-to-year base. The mapfigures show indifferentcolours the stationsthat

40

belongtoeachassemblage;noattempthasbeenmade10drawanycontours.Thesemaps shouldbecompared10themeansituation(Fig.4-1 ) where contoursweredrawn mo re to setuplimitsthan 10cha racterize anyspecificyean 'distri butionoftheassemblages.

Yellowdotsrepresent sta tionstha tbelongto theso-calledDeepAssemblage,redare Mainstations,NorthAiSemblageisrepresentedbyblackdotsand orangeisused forthe Coastalstations;thedotisplacedintheexactlatit udeandlongi tude of thestation sampled. Thedifferentblue tonesof the backgroun d represen tthe bathyme tryof the arearanging fromwhite(O-I oom)to lightblue(200 m)andincreasingly darke r blue unt il

>800m.The basemapco versla ti tudes (4S"Nto 55°SO'N)and long itudesfrom49° W toS9"Wincluding thereforeNAFOareas 2Jand 3K in theirentirety.

Autumn 1978

This year ' scruise containsthelowest numberof statio ns.especiallyfor theDeep and Coasta l Assemblages (GIS map of1978). Itpresentsingeneralan average diwibution patternthough the depthof thenaionsthatco mprisethe Maingroupare somewhatshallower(392mwasthedeepeststationsampled inthisgroup) tha nnormal;

even50itshowedthe gene raltrendbecausethedeepeststationmeasuredin the whole areawas ooly400mdeep.Witchflounderappears intheDeepgroup(hisyearwithS leg/towtaken,probablydue tosamp!in.. .iyshallowerstations. TheCPUEof Greenland HalibutinthcCoastalAssemblagehuavaluemuchgreaterthanthe meanfor alltheyearsandwastheonlyoccasionwhenover 100kgofthisspecieswere caughtin this group(115kg/tow),SPOiledandStripedwolffi shappearatahigherCPUEthan any otheryea rintheMaingroup; thesameoccursforthe latter intheNo rthAssemblageand for Roughheadgrenadierin theDeepgroup . Arctic cod show sitshigherabundance in theMaingroupin1978100.ColderIhan averagesurfacetemperaturewerefoundinthe Northand CoastalAssemblages.

Autumn 1979

Stauonswith thecharacteristics oftheNorth groupappeared very farsouththis

41

year, reachinglatitudesof 50"30'N .The Main Assemblageextends slightlynorthwards appearing north of Hawke Saddleand occupyingthe area normally belonging to the North Assemblage. Somevery deep stationsweremeasuredwithin the DeepAssemblage reaching 1334m to theeast of the slope break. Mainand Northgroupsexhibitedvery lowvalues for Atlanticcod.No Arcticcodwere found in the Coastal Assemblage.The highestCPUE for Roundnosc grenadierin the Deep group over allyears occurred in 19 79 (72 kg/tow).

Aulumn 1980

Thereis certain intrusionofthe Deep Assemblageintothe area of the North Assemblage along CartwrightSaddlewithIhe resultthat the mean boucmte mpera ture is unusuallylowin the Deepgroup.The North Assemblageextends southwards reaching thesouthernpari of theFunkIsland Deep.Theother assemblages remained as in the mean situation. Goldenredfish shows itspeak inthe Main Assemblageduringthisyear reaching nearly60kg/tow;the same occurs forRoughheadgrenadierinthe Nonh Assemblagebut in muchlower abundance,Arcticeetpoutdisappears thisyear fromthe assemblageswhereasBroadheadwolffishreachesa maximumCPUE for all years in the Deepgroup;the same applies to Thornyskate in theNorth group. Marlin spike,a component in low abundance in the Deep group appears more abundantin 1980lllanin therest orthe years,

Autumn 1981

TheCoastalAssemblageappeared mainlytothe south in NAFO area 3K with only 2 stations in 2J,The Nonh groupinvaded the CoastalAssemblagearea in2J, Thorny skate and Americanplaiceincreased to their peak abundancein the Coastal group thisyear and maintainedthis abundance through1982,In 1981,the highestCPUB for Deepwaterfoolish was found.with430 kg/lOWbeingcaught in the Deep group.

42 Aulu m n 1982

Northstations kttpintnidingintoareasmorenormallyCoastal.especia11yaround latitude53-30'N .Therestofthesitua tionis equivalent10 lhe mean. ColdertIw\

averag ebottomtempera ture occurredfor theCoastaland NorthAsse mblag es.Thisis acoldsurfacetemperatureyear forlheMain Assemblage butiswarmerthanusualfor theNonh.HighestvaluesofabundanceofAmericanplace. Broadheadwolffish,Spotted wolffis handArctic eelpoutin theNorth groupover allyeanoccur in1982.

Autumn 1983

In contrastto1982,itistheCoastalAssemblagethat startsinvading theNorth group area,especially onthe westernpartofHamilton Bank.The NorthAssemblage elongatessoothwardsreachingagainlatitudes ofSooN,similartothesituationinthefall of1979.Bottomtemperatureswereeven colderfortheCoastaland NorthAssemblages.

bUIwere the warmestencountered sofarfor theDeepAssemblage. Greenlandhalibut abundance diminishedgreatly to lessthan halfthatfoundpreviouslyintheCoastal Assemblage. Anolher~trongpeakofabundanceoccursin Deepwaterredfishwith)40 kg/tow caught inthe:Main group,largelytheresultoftwovery large catches at286m (11,050kg)and 344 m (I1,948 kg).Stripedwolffish reaches itsmaximumCPUEin the Northgroup in1983.

Aulumn1984

St.Anthony Basinand Hamilton Bank,areas thatformerlyhad stations characteristic ofthe NorthandMain Assemblagesarebeingtakenoverbythe Coastal Assemblage. TheNorthandCoastalAssemblages continued tohaveverylowmean bottom temperatures and theDeepAssemblage appears cooler too . Thesurface temperature hasdecreased inall the groups.This yearAtlantic cod showsthemaximum CPUEoverall yearsinthe CoastalAssemblageand Thornyskatein the Main;

furthermore,Greenlandhalibulin theNorthnearlyrecoversto its maximum of12:S